This application claims the benefit of the Korean Application No. P2000-84717 filed on Dec. 28, 2000, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a projector.
2. Background of the Related Art
The projector enlarges, and projects a small picture on a small display inside of the projector by using a lens system to a large sized screen, to display a large sized picture. There are a front projection type in which the picture is displayed on a front face of the screen, and a rear projection type in which the picture is displayed on a rear face of the screen. As a typical one of the latter, there is the projection television. As the small display in the projector that displays the small picture, LCD (Liquid Crystal Display) and DMD (Digital Micromirror Device), and the like are employed. The LCD is provided with a polarization beam converter for displaying the picture by using a linearly polarized light. FIG. 1 illustrates a related art projector.
Referring to FIG. 1, the related art projector is provided with a lamp 1 for emitting a beam of light, a parabolic reflector 2 for reflecting the beam to forward of the lamp 1, a polarization beam converter for transmitting an xe2x80x98Sxe2x80x99 wave, and converting xe2x80x98Pxe2x80x99 wave into xe2x80x98Sxe2x80x99 wave and transmitting the converted xe2x80x98Sxe2x80x99 wave among the beam from the parabolic reflector 2, first to third illumination lenses 10, 12, and 14 for focusing the beam polarized into a particular polarized light at the polarization beam converter, a color switch 16 for transmitting only a particular beam among the beams from the third illumination lens 14, a polarization beam sprite prism 18 for supplying a color light from the color switch 16 to a display 22, and the beam reflected at the display 22 to a projection lens 20, a display 22 for displaying a picture by reflecting the color light from the polarization beam sprite prism 18 in response to a video signal, and a projection lens 20 for enlarging the beam of the picture from the display 22, and projecting to a distance.
The beam of light from the lamp 1 is directed to the polarization beam converter by the parabolic reflector 2. The polarization beam converter transmits the S wave, and converts and transmits P wave among the beam from the parabolic reflector 2.
To do this, the polarization beam converter is provided with a first lens array 4, a second lens array 6, and a polarization beam sprite array 8 facing a light output surface of the second lens array 6. The first lens array 4, or the second lens array 6 focuses the beam of light including the P wave and the S wave to a plurality of focusing points.
To do this, the first, or second lens array 4, or 6 has a matrix of a plurality of lenses. The polarization beam sprite array 8 transmits xe2x80x98Sxe2x80x99 wave, and converts the P wave into the S wave, and transmits the converted S wave, both from the second lens array 6. To do this, the polarization beam sprite array 8 provided with polarization beam split planes 24 and reflection planes 26, and half wave plates 28 attached to light output surfaces of the polarization beam split planes 24 as shown in FIG. 2.
The polarization beam split plane 24 transmits only the P wave and reflects the S wave among the white light from the second lens array 6. The P wave transmitted through the polarization beam split plane is converted into an S wave by the half wave plate 28. On the other hand, the S wave reflected at the polarization beam split plane 24 is reflected at the reflection plane 26.
That is, the entire beam of light including the P wave and the S wave passed through the polarization beam sprite array 8 is converted into the S wave. The beam of light converted into the S wave at the polarization beam converter passes through the first to third illumination lenses 10, 12, and 14 in succession. The first to third illumination lenses 10, 12, and 14 focus the beam of light converted into the S wave onto the color switch 16.
The color switch 16 splits red, green, and blue colors in succession so that one display cell has red, green, and blue colors. To do this, the color switch 16 filters a particular color light according to a variation of a voltage signal applied. In this instance, the color light passed through the color switch 16 is converted into the P wave from the S wave, and directed to the polarization beam sprite prism 18. The P wave color light from the color switch 16 to the polarization beam sprite prism 18 transmits a split plane 30, and directed to the display 22.
The display 22 reflects the P wave color light transmitted through the polarization beam sprite prism 18 according to a video signal, to produce a picture beam with picture information. In this instance, as shown in FIG. 3A, the P wave color light reflected at the display 22 is converted into the S wave when no electric signal is applied thereto.
The picture beam converted into the S wave at the display 22 is reflected at the split plane 30 of the polarization beam sprite prism 18, and directed to the projection lens 20. To do this, the split plane 30 of the polarization beam sprite prism 18 transmits the P wave, and reflects the S wave as shown in FIGS. 4A and 4B. Accordingly, the polarization beam sprite prism 18 transmits the P wave from the color switch 16, and reflects the S wave from the display 22 toward the projection lens 20. The projection lens 20 enlarges the picture beam from the polarization beam sprite prism 18, and projects to a screen at a distance.
In the meantime, as shown in FIG. 3B, the display 22 transmits the P wave color light from the polarization beam sprite prism 18 is if there is an electrical signal applied thereto. Therefore, no beam of light is incident on the projection lens 20 when there is the electrical signal applied to the display 22. The projection lens 20 enlarges the picture beam from the polarization beam sprite prism 18, and projects onto a screen at a distance therefrom.
However, the color switch 16 for splitting the color light from the beam of light in the related art projector has a poor light efficiency caused by poor light transmission performance. A color wheel may be employed in place of the color switch 16.
However, for employing the color wheel in the related art projector, an optical system that converges the beam of light and an optical system that diverges the beam of light are required. Moreover, the polarization beam converter in the related art projector requires lens arrays 4, and 6 each having a plurality of lenses.
However, the lens array 4 or 6 with the plurality of lenses has optical losses between the lenses. A number of the lenses in the lens array 4 or 6 may be reduced for reducing the optical loss, but that increases a thickness of the polarization array to push the cost up. Moreover, since an optical conversion efficiency is significantly dependent on an alignment of the lens arrays 4, and 6, assembly of the projector requires much time.
In addition to this, the related art projector has the lamp with the parabolic reflector 2 for providing parallel lights to the polarization beam converter. The lamp with the parabolic reflector 2 has an optical efficiency poorer than a lamp 34 with an elliptic reflector 32 as shown in FIG. 5.
It will be explained in detail assuming that a diameter of the parabolic reflector 2 is Dp and a diameter of the elliptic reflector is De. The lamp 1 with the parabolic reflector 2 directs the beam of light forward in parallel, i.e., the parabolic reflector 2 is required to have a slope for directing the beam from the lamp 1 forward in parallel.
On the other hand, the lamp 34 with an elliptic reflector 32 directs the beam of light such that the beam is focused at a plane in front of the lamp 34. Accordingly, the elliptic reflector 32 is required to have a slope greater than the parabolic reflector 3 so that the beam from the lamp 34 is focused on the plane in front of the lamp 34. That is, because the lamp 34 with the elliptic reflector 32 can reflect more beam, the lamp 34 with the elliptic reflector 32 has an optical efficiency higher than the lamp 1 with the parabolic reflector 2.
If the lamp 34 with the elliptic reflector 32 and the lamp 1 with the parabolic reflector 2 have the same optical efficiency, the diameter of the elliptic reflector 32 can be made smaller than the parabolic reflector 2, to reduce a size of the elliptic reflector 32. However, since the related art polarization beam converter requires a parallel light, the lamp 34 with the elliptic reflector 32 can not be employed.
Therefore, the related art projector has a limitation in fabricating a thinner projector. Moreover, because the related art projector splits red, green, and blue lights from the beam of light, a quantity of light only in a range of ⅓ can be used. For increasing such a lack of quantity of light, though it is required to make a waveband of the light greater, the greater waveband makes a purity of a color poor.
Moreover, it can be known from a spectrum distribution of a light source of the related art projector that a red color lacks in quantity, substantially. Nevertheless, the related art projector has no means to remedy the lack of particular light, particularly, the red light.
Accordingly, the present invention is directed to a projector that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a projector which can improve a color purity and an optical efficiency.
Another object of the present invention is to provide a projector which permits fabrication of a thin projector.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the projector includes a light source, a color wheel for splitting two, or more than two color beams from the beam from the light source, a rod lens for making a distribution of the color beam from the color wheel uniform, a polarization beam converter for converting the color beams into particular polarization beams, an optical system for focusing the color beams converted into the particular polarization beams, a color selecting plate for converting particular polarization color beams in the focused color beams, a first display and a second display for reflecting the color beams from the color selecting plate according to a video signal to form different picture beams, a polarization beam sprite prism for supplying a particular color beam having polarization converted at the color selecting plate to the first display, and color beams of other colors to the second display, and a projection lens for enlarging, and projecting the picture beams.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.